Comparison of effect of a panel of membrane channel blockers on the proliferative, cytotoxic and cytoadherence abilities of human peripheral blood lymphocytes

Abstract

The ability of human peripheral blood lymphocytes (PBMNC) to incorporate tritiated thymidine upon stimulation with concanavalin A, to perform natural cytotoxic (NK) activity and to form types of spontaneous “rosettes” with sheep red blood cells (SRBC) upon in vitro treatment with membrane channel blockers of different specificity was estimated. All five channel blockers used, i.e., verapamil, nifedipine, diltiazem, saxitoxin and tetraethylammonium exerted a biphasic, dose-dependent effect on the Con A-induced proliferation of PBMNC. Verapamil, saxitoxin and nifedipine significantly increased the percentage of PBMNC forming spontaneously “active” rosettes with the SRBC. All channel modifiers tested for this ability decreased the percentage of PBMNC forming “late” rosettes. Natural killer activity was significantly decreased in the presence of micromolar concentrations of calcium antagonists as well as when the cells were treated with tetraethylammonium. The results of all four parameters tested were also compared with these obtained in a group of patients treated with 300 mg per day verapamil for two weeks preceding the tests. In this case we have found that treatment in vivo significantly decreased the response of PBMNC to mitogen stimulation, but it was without effect on either NK cytotoxicity or rosette formation. Cells of verapamil-treated patients did not show increased response to Con A in the presence of low concentration of the blocker in vitro. Also, they were not able to form more “active” rosettes when treated with 1–100 nM verapamil. We believe that apparent bi-directional pattern of action of calcium, sodium and potassium channel blockers on the proliferation and rosette formation of human PBMNC can be explained by two sets of events producing opposite results. First, we suggest that at respectively low concentrations of the blockers all of them generate uniform modulation of transmembrane electrical potential (depolarization) of lymphocytes. Depolarization promotes cell adhesion and is probably beneficial for early stages of the response to mitogen. At higher concentrations, this effect is overshadowed by other pharmacological actions of the blockers, of mostly inhibitory character.